1. Field of the Invention
The present invention relates to DC-DC converter modules including a DC-DC converter provided on a multi-layer substrate, and multi-layer substrates.
2. Description of the Related Art
Power supply circuits for portable devices use a linear regulator type or switching regulator type ultra compact regulator module. A linear regulator type module has a low voltage conversion efficiency since all the voltage variation components are converted into heat, and a switching regulator type module has inferior noise characteristics due to switching noise or the like. Hence, it is desired that a DC-DC converter that has a high voltage conversion efficiency and good noise characteristics be reduced in size so as to be usable in a power supply circuit of a portable device or the like.
To reduce the size of a DC-DC converter, the DC-DC converter may be formed in a multi-layer substrate including a magnetic body therein (refer to, for example, Japanese Unexamined Patent Application Publication No. 2006-42538 and Japanese Patent No. 4325747).
FIG. 1 is a diagram illustrating an existing configuration of a DC-DC converter module. A DC-DC converter module 101 includes a magnetic substrate 102, a switching IC 103, and a capacitor component 104. The bottom surface of the magnetic substrate 102 has input/output terminals (not illustrated) and a ground terminal GND formed thereon and the top surface has the switching IC 103 and the capacitor component 104 mounted thereon. The substrate has a coil 106 formed therein.
In the existing DC-DC converter module, a wiring line that connects the ground electrode connected to the ground potential of a board on which the module is mounted to the switching IC mounted on the module also extends through the magnetic substrate. Hence, the impedance of the wiring line becomes high and the potential of the ground port of the switching IC is likely to be different from the actual ground potential.
In addition, since a wiring line between the switching IC and a coil through which a saw tooth or pulse current flows is near the ground port of the switching IC, the wiring line and the ground port are coupled to each other, causing noise transmission. Hence, the potential of the ground port may vary significantly, resulting in a high noise level in the converter output.